For the short pastry, knead 300 g flour, 150 g butter in pieces, 1 egg, 1 pinch of salt and 2 tablespoons of ice-cold water, first with the dough hooks of the mixer, then with your hands to form a smooth dough. Cover and chill for about 30 minutes.
In the meantime, dice the bacon. Peel the onions and cut them into thin rings. Heat the oil in a pan. Fry the bacon in it for 3-4 minutes until crispy, take it out. Fry the onions in 2-3 portions in hot frying fat at low heat for about 10 minutes until they are glassy, they must not get brown.
Let it cool down.
Grease a tart mould with a removable base (approx. 28 cm Ø) and dust with flour. Preheat the oven (electric cooker: 175°C/circulating air: 150°C/gas: level 2). Roll out the dough on a little flour until round (approx. 32 cm Ø).
Line the mould with it and press it on the edge to a height of approx. 2 cm.
Place baking paper on the dough and fill with the pulses. Bake blind in a hot oven for about 10 minutes (stabilises the edge of the dough). Then remove the pulses together with the baking paper.
Bake the dough for 8-10 minutes. Then remove from the oven.
Whisk the crème fraîche, milk and 4 eggs. Season with salt and pepper. Spread the onions on the dough, sprinkle with bacon. Pour egg icing over it. Bake in a hot oven at the same temperature for 30-40 minutes.